1. Field of the Invention
The present invention relates to a system for controlling the hydraulic line pressure in an electronic automatic transmission, and more particularly to a pressure regulator having a solenoid-actuated valve for adaptively controlling the hydraulic line pressure to frictional elements within the transmission based on the slip through the transmission.
2. Description of Related Art
Generally speaking, land vehicles require three basic components--a power plant such as an internal combustion engine, a powertrain and wheels. The function of the powertrain is to transmit torque generated by the power plant to the wheels thereby providing movement of the vehicle. A powertrain's main component is typically referred to as the transmission. Engine torque and speed are converted in the transmission in accordance with the tractive power demand of the vehicle to propel the vehicle. The vehicle's transmission is also capable of controlling the direction of rotation being applied to the wheels so that the vehicle may be driven both forward and backward.
An automatic transmission typically includes a hydrodynamic torque converter to smoothly transfer engine torque from the engine crankshaft to the transmission input shaft through fluid flow forces. The transmission also includes frictional elements or clutch assemblies which couple the transmission input shaft through one or more planetary gear sets to provide various ratios of torque to the transmission output shaft. The output shaft is usually connected to the drive wheels via a differential.
A hydraulic control assembly engages and disengages the frictional elements which transfer torque through the transmission and effect gear changes in the transmission. Various components, such as spring-biased spool valves, spring-biased accumulators and ball check valves, direct and regulate the fluid flow in the hydraulic control assembly. A hydraulic pump provides fluid pressure and flow rate to energize the hydraulic components in the assembly. Sufficient hydraulic line pressure is required to engage the frictional elements and prevent slippage therebetween to transmit torque from the transmission input shaft to the transmission output shaft. If insufficient line pressure is provided, the frictional elements do not fully engage and slip occurs resulting in power loss through the transmission. Conversely, if excessive line pressure is provided, the hydraulic pump torque is higher than necessary resulting in decreased fuel efficiency of the vehicle.
It is well known that a fixed displacement pump and a pressure regulator may be used to maintain the appropriate line pressure. These systems rely on springs to provide a predetermined fluid flow rate and pressure for various operating conditions. Thus, once the transmission is designed, the operating conditions of the hydraulic system is fixed. It is also well known to use a variable displacement pump in place of the fixed displacement pump and pressure regulator. These pumps are considerably more costly than fixed displacement pumps.
A thorough description of general automatic transmission design principles may be found in "Fundamentals of Automatic Transmissions and Transaxles," Chrysler Corporation Training Manual No. TM-508A. Additional descriptions of automatic transmissions may be found in co-assigned U.S. Pat. No. 3,631,744, entitled "Hydrodynamic Transmission," issued on Jan. 4, 1972 to Blomquist, et al., and U.S. Pat. No. 4,289,048, entitled "Lock Up system for Torque Converter," issued on Sep. 15, 1981 to Mikel, et al. These patents are hereby incorporated by reference.
In recent years, a more advanced form of transmission control system has been proposed, which offers the possibility of enabling the transmission to learn and adapt itself to changing conditions. In this regard, co-assigned U.S. Pat. No. 3,956,947, issued on May 18, 1976 to Leising, et al., sets forth a fundamental development in this field and is hereby incorporated by reference. Specifically, U.S. Pat. No. 3,956,947 discloses an automatic transmission design which features an adaptive control system that includes electronically operated solenoid-actuated valves for providing closed-loop control of various functions in the hydraulic control assembly.
3. Objects of the Present Invention
It is one of the principal objects of the present invention to provide a system for continually controlling the hydraulic line pressure in an automatic transmission such that the minimum line pressure necessary for full engagement of the frictional elements based on the characteristics and current operating condition of the automatic transmission improving transmission efficiency thereby increasing the fuel economy of the vehicle.
Another object of the present invention is to provide a control system for controlling hydraulic line pressure based on the torque input to the transmission.
A further object of the present invention is to provide an adaptive system for controlling the hydraulic line pressure.
It is another object of the present invention to provide a method for controlling the hydraulic line pressure in an automatic transmission such that a minimum required line pressure is provided to frictional elements to prevent them from slipping improving transmission efficiency, thereby increasing the fuel economy of the vehicle.
An additional object of the present invention is to provide a method for adaptively controlling the hydraulic line pressure, such that corrections to the methodology are incorporated based on prior operational conditions of the transmission operation.
Still another object of the invention is to provide a closed-loop control system where the control actuation can be continuously corrected as opposed to an open-loop control system in which signals to various elements are processed in accordance with a predetermined program.